The invention relates to information networks or systems which allow messages to be exchanged between posts or stations.
It relates more precisely, but not exclusively, to networks wherein the transmission is of the xe2x80x9cradio-frequencyxe2x80x9d type, i.e. those which require no connections known as xe2x80x9chardware supportxe2x80x9d or xe2x80x9cwiresxe2x80x9d (such as for example cables or fiber optics).
Networks of this kind, which may be termed local, are easy to install, but they do have a drawback connected with the limited range of the transmissions, typically a few dozen meters for outputs of several Megabits per second. This limitation, which is due chiefly to the laws of physics which govern radio transmissions, is impossible to circumvent.
Those skilled in the art have proposed certain solutions for overcoming this problem, such as for example increasing the broadcasting power, or improving reception by the use of booster aerials.
As regards local networks, in particular, it is common to use stations which are at least a hundred meters apart. Some of these networks have a conventional structure in which the stations are connected at level xe2x80x9c2xe2x80x9d, such as for example the MAC level or LLC level of the ISO model of OSI. More precisely, the stations comprise an operating system, a stage (or layer) known as xe2x80x9cnetworkxe2x80x9d which processes and generates messages of a first format, a communications card for exchanging messages of a second format with other stations which belong, generally speaking, to the same network, a so-called xe2x80x9ccontrolxe2x80x9d stage (known in English as the xe2x80x9cdriverxe2x80x9d, such as the MAC driver, in particular) for putting messages received from the card or the network stage, respectively, into the first format or into the second format and transmitting them to the network stage or to the card, and means for interfacing the stages, card and operating system with one another (normally software and/or connecting cables).
In this type of network, the solution proposed for relaying messages (or frames) consists in using at level 2 of each station techniques as described in FR patent 9509928 by this Applicant. These techniques require so-called xe2x80x9cintelligentxe2x80x9d network cards which have their own hardware and software resources. Cards of this kind are complex and expensive, which runs counter to practice in wired networks where the cards are simple in design.
The aim of the invention is therefore to provide a system for transmitting messages, and the corresponding process, which do not have the drawback mentioned above.
To this end it proposes a system of the type described in the introduction, wherein at least some stations have a management stage coupled to their operating system by interface means and placed between their network stage and their driver stage so as to carry out one and/or other of the following operations a) and b):
a) intercepting messages in the first format which have to be exchanged by the network stage and the driver stage (in the xe2x80x9cascendingxe2x80x9d direction and in the xe2x80x9cdescendingxe2x80x9d direction), in order to analyse the data they contain and decide to continue transmitting them between stages, subject to any processing, as a function of at least one criterion bearing on the data analysed,
b) generating, spontaneously or on request, messages of a selected type, in the second format, such as for example service messages, with a view to sending them through the network via the communications card when a selected condition is met.
The definition xe2x80x9cascendingxe2x80x9d refers to a message (or data) coming from the driver stage and directed towards the network stage, whereas xe2x80x9cdescendingxe2x80x9d refers to a message (or data) coming from the network stage and directed towards the driver stage.
Thanks to the invention, the management stage can absorb an ascending message (e.g. qualitatively filter or extract information relating only to itself), and/or generate a descending message in order to add data thereto or to generate another descending message, and/or intercept an ascending message in order to relay (or route) it, i.e. convert it into an at least partially modified descending message and possibly transmit it jointly to the network stage.
Thus, by xe2x80x9cdecision to continue transmissionxe2x80x9d is meant a decision to convert an ascending message into a descending message, or a decision to continue the descent/ascent of a descending/ascending message, or a decision to convert an ascending message into a first ascending message and a second descending message, or a decision to interrupt the ascent of an ascending message with the purpose of using its information in the management stage (this applies particularly to service messages).
Thus, the communications card (or network card), the driver stage and the network stage (or layer) of a station may be retained without modifying their respective equipment and software.
Preferably, the operating system of the stations provided with a management stage is of the multi-task type, so that some of the processing power and the memory of the station are used for managing the connection of this station to the network, without this interfering with other applications (or tasks).
According to another feature of the invention, the messages in the second format comprise a first field (preferably formed by at least the address of the final destination station, and more preferably a first pair of addresses preferably comprising the addresses of the initial originating station and the final destination station). This first field may be replaced or, preferably, supplemented by a second field forming a xe2x80x9ccapsulexe2x80x9d or part of a capsule, and preferably made up of at least one address of an intermediate destination station, and better still a second pair of addresses preferably comprising the address of the last station to have emitted the message received (known as the intermediate originating station) and the address of the intermediate destination station.
According to another feature of the invention, the messages in the second format may comprise data representing the type of information which they contain. In this case, the criterion chosen for the decision to continue transmission advantageously relates to the type of information contained in the messages received from one stage of the station.
According to a further feature of the invention, the messages in the second format may include data representing their sequence numbers.
According to the invention, the management stage is capable of ensuring at least one function (or treatment) selected from the encapsulation/de-encapsulation of messages to be transmitted or received, the generation of service messages, either spontaneously or on request, the routing of information, the synchronisation of the station in which the management stage is installed and possibly that of other stations in the network to which this station is connected.
The term xe2x80x9croutingxe2x80x9d here means determining an intermediate station address in order to (re)transmit a message in the optimum manner to one or more final destination stations, by interrogating a routing table stored in the management stage, this table being capable of being updated using topological data and/or neighbourhood data supplied by the service messages emitted by the other stations of the network.
Moreover, de-encapsulation/encapsulation refers to the removal from a message, or the addition thereto, of a capsule consisting in particular of a pair of addresses.
Moreover, the term synchronisation denotes the xe2x80x9calignmentxe2x80x9d of at least the transmitting/receiving means of the station with the frequency transmission mode and the reference time common to the network or at least one of its stations, so that at least the relay stations of the network are all synchronised. This synchronisation may be implemented using the synchronisation messages received from the other stations, but it may also be initiated by the driver stage of a station.
The invention also applies to stations equipped with at least two driver stages each respectively connected to, on the one hand, communication cards connected to different networks and, on the other hand, the management stage, which is capable of selecting one and/or the other of the networks with a view to transmitting a message according to the address of the intermediate destination station contained in the message which is to be transmitted. In this case, one of the networks is of the radio type whereas the other network(s) are preferably of the wired type. Thus, it is possible to use a wired network as a shortcut, or as an emergency solution when radio transmission proves impossible.
According to yet another feature of the invention, when the management stage is arranged to perform at least two different functions (or processes), it preferably comprises switching means connected to the means which perform these functions, which are capable of switching the messages (or data) depending on the type of information which they contain.
The invention also proposes a process for transmitting messages (or data or frames) between the stations of a system of the type described hereinbefore, comprising one and/or the other of the following steps:
intercepting each message which is to be exchanged between the network stage and the driver stage of a station, then analysing the information contained in the intercepted message in order to decide on continuing its transmission, possibly after processing, as a function of at least one criterion bearing on the information analysed,
generating a message of a selected type for broadcast on the network when a selected condition is met.